Permafrost Stores a Globally SignificantAmount of MercuryPaul F. Schuster1 , Kevin M. Schaefer2 , George R. Aiken1,3, Ronald C. Antweiler1 ,John F. Dewild4 , Joshua D. Gryziec5, Alessio Gusmeroli6 , Gustaf Hugelius7 , Elchin Jafarov8 ,David P. Krabbenhoft4 , Lin Liu9 , Nicole Herman-Mercer1 , Cuicui Mu10 , David A. Roth1 ,Tim Schaefer11, Robert G. Striegl1 , Kimberly P. Wickland1 , and Tingjun Zhang10

1U.S. Geological Survey, National Research Program, Boulder, CO, USA, 2National Snow and Ice Data Center, CooperativeInstitute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA, 3Deceased, 4U.S.Geological Survey, Wisconsin Water Science Center, Mercury Research Laboratory, Middleton, WI, USA, 5EnvironmentalService Lab, Broomfield, CO, USA, 6International Arctic Research Center, University of Alaska, Fairbanks, AK, USA,7Department of Physical Geography, Stockholm University, Stockholm, Sweden, 8Computational Earth Sciences, LosAlamos National Laboratory, Los Alamos, NM, USA, 9Earth System Science Programme, Faculty of Science, ChineseUniversity of Hong Kong, Hong Kong, 10Key Laboratory of Western China’s Environmental Systems (MOE), College of Earthand Environmental Sciences, Lanzhou University, Lanzhou, China, 11Galmont Consulting, Chicago, IL, USA

Abstract Changing climate in northern regions is causing permafrost to thaw with major implications forthe global mercury (Hg) cycle. We estimated Hg in permafrost regions based on in situ measurements ofsediment total mercury (STHg), soil organic carbon (SOC), and the Hg to carbon ratio (RHgC) combinedwith maps of soil carbon. We measured a median STHg of 43 ± 30 ng Hg g soil�1 and a median RHgC of1.6 ± 0.9 μg Hg g C�1, consistent with published results of STHg for tundra soils and 11,000 measurementsfrom 4,926 temperate, nonpermafrost sites in North America and Eurasia. We estimate that the NorthernHemisphere permafrost regions contain 1,656 ± 962 Gg Hg, of which 793 ± 461 Gg Hg is frozen in permafrost.Permafrost soils store nearly twice as much Hg as all other soils, the ocean, and the atmospherecombined, and this Hg is vulnerable to release as permafrost thaws over the next century. Existing estimatesgreatly underestimate Hg in permafrost soils, indicating a need to reevaluate the role of the Arctic regionsin the global Hg cycle.

Plain Language Summary Researchers estimate the amount of natural mercury stored inperennially frozen soils (permafrost) in the Northern Hemisphere. Permafrost regions contain twice asmuch mercury as the rest of all soils, the atmosphere, and ocean combined.

1. Introduction

Over thousands of years, sedimentation buried mercury (Hg) bound to organic material and froze it into thepermafrost (Obrist et al., 2017). Permafrost is soil at or below 0°C for at least two consecutive years. Theactive layer is the surface soil layer on top of the permafrost that thaws in summer and refreezes in winter(Figure S1 in the supporting information). Hg deposits onto the soil surface from the atmosphere, where itbonds with organic matter in the active layer. Microbial decay then consumes the organic matter, releasingthe Hg (Smith-Downey et al., 2010). At the same time, sedimentation slowly increases soil depth such thatorganic matter at the bottom of the active layer becomes frozen into permafrost. The organic matter con-sists almost entirely of plant roots, and, once frozen, microbial decay effectively ceases, locking the Hg intothe permafrost. However, permafrost has begun to thaw under a changing climate (Hinzman et al., 2005;Romanovsky et al., 2008; Smith et al., 2010). Once the permafrost and associated organic matter thaws,microbial decay will resume and release Hg to the environment, potentially impacting the Arctic Hg balance,aquatic resources, and human health (Dunlap et al., 2007; Jonsson et al., 2017; Obrist et al., 2017; USGS FactSheet, https://www2.usgs.gov/themes/factsheet/146-00/, 2016). Model projections estimate a 30–99%reduction in the area of Northern Hemisphere permafrost by 2100, assuming anthropogenic greenhousegases emissions continue at current rates (Koven et al., 2013). In a novel approach, we make the first-everestimate of the storage of Hg in the Northern Hemisphere permafrost soils using empirical relationshipsbased on in situ measurements of sediment total mercury (STHg) combined with published maps of soilorganic carbon (Hugelius, Tarnocai, et al., 2013; Hugelius, Bockheim, et al., 2013).

SCHUSTER ET AL. PERMAFROST STORES A GLOBALLY SIGNIFICANT AMOUNT OF MERCURY 1

PUBLICATIONSGeophysical Research Letters

RESEARCH LETTER10.1002/2017GL075571

Key Points:• Permafrost stores a significant amountof mercury

• Permafrost regions store twice asmuch mercury as all other soils, theocean, and atmosphere combined

• Thawing permafrost in a warmingclimate may release mercury to theenvironment

Supporting Information:• Supporting Information S1• Data Set S1• Data Set S2

Correspondence to:P. F. Schuster,pschuste@usgs.gov

Citation:Schuster, P. F., Schaefer, K. M., Aiken,G. R., Antweiler, R. C., Dewild, J. F.,Gryziec, J. D., … Zhang, T. (2018).Permafrost stores a globally significantamount of mercury. GeophysicalResearch Letters, 45. https://doi.org/10.1002/2017GL075571

Received 27 SEP 2017Accepted 10 JAN 2018

©2018. American Geophysical Union.All Rights Reserved.

2. Site Descriptions and Methods

To estimate Hg in permafrost regions, we drilled 13 permafrost soil cores of variable lengths in Alaska along a~500 km north-south transect representing a broad array of characteristics and ages typical of circumpolarpermafrost soils (Figures 1 and S2–S10 and Tables S1 and S2). The maximum depths varied between 98and 248 cm below the land surface, and the sites reflect a variety of depositional conditions. For each corewe dug a pit down to the top of the permafrost and measured active layer depth (ALD). We extracted thecores using a gas-powered Snow, Ice, and Permafrost Research Establishment (SIPRE) auger modified withcarbide cutting blades for frozen soil (Figure S11). The SIPRE can drill to a maximum depth of ~2 m, butobstructing rocks typically limited the actual drilling depth at each site. We broke each core into smallersamples, which we photographed, wrapped, labeled, and stored in a portable freezer (Figure S12). Weshipped the frozen cores to the U.S. Geological Survey (USGS) Research Laboratory in Boulder, Coloradoand stored them at �20°C until cutting, processing, and analysis.

We cut the cores in half lengthwise using a band saw thoroughly cleaned with methanol and 18 MegaOhmdeionized water and archived one half in airtight bags in a freezer for future analyses (Figures S13 and S14).We then sliced the frozen cores into 1.5 cm segments for a total of 588 samples (Figure S15). We followedstandard techniques of trace metal sampling with laboratory technicians wearing Latex gloves at all times(U.S. Geological Survey, 2015). Using a ceramic knife on a Teflon surface, we cut each frozen segment into

Figure 1. Locations of permafrost coring sites (black circles) and sites from other published studies (red circles) superimposed on a map of permafrost regions.

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two rectangular subsamples from the center of the segment, one for STHg and one for bulk density (BD). Wescraped off the outer fewmillimeters of the Hg subsample with the knife before measuring STHg (Figure S16).We weighed andmeasured the dimensions of the larger subsample to determine BD (Soil Survey Staff, 2014).We placed the STHg subsample in a preweighed, Hg-free jar, recorded the mass, and freeze-dried it(Figure S17). We thoroughly cleaned a mortar and pestle with 18 MegaOhm deionized water, homogenizedthe Hg subsample to a fine powder, and stored the powder in Hg-free glass vials (Figure S18).

We measured STHg, BD, soil organic carbon (SOC), and Δ14C and calculated the Hg to carbon ratio (RHgC)(Table S3). Quality Assurance and Control accounted for more than 56% of all analyses (Texts S1–S3). Wesplit every tenth segment into duplicate subsamples (Figure S19). For the CF and EG cores, we analyzedSTHg at the USGS Mercury Research lab in Madison, Wisconsin using EPA Method 7473 (EPA Method7473 (SW-846), 1998; USGS Mercury Research Lab (MRL), http://wi.water.usgs.gov/mercury-lab/analysis-methods.html, 2013). For all other cores, we measured STHg using a Milestone Direct Mercury Analyzer-80 (DMA-80) at the USGS Research Laboratory in Boulder, Colorado (Figure S20, Text S4, and Table S4).For soil carbon dating, we give Δ14C concentration as the fraction Modern Δ14C and conventional radio-carbon age (Text S5). We measured loss on ignition (LOI) for the second subsample as the loss of weightof a dried sample ignited at 550°C for 5 h by a Muffle furnace (Soil Survey Staff, 2014). To estimate SOC,we multiplied LOI by a carbon fraction of 0.493 (Anderson & Sarmiento, 1994). We used the standardRedfield ratio of 0.493 based on the 117:14:1 C;N;P; ratio of marine biomass samples. We calculatedRHgC as the ratio of STHg to SOC for each sample (Bargagli et al., 2007).

To create maps of soil Hg, we multiplied maps of soil carbon by a representative RHgC. We used soil carbonmaps from the Northern Circumpolar Soil Carbon Database (NCSCD) at a spatial resolution of 0.5° latitudeand longitude (Hugelius, Tarnocai, et al., 2013; Hugelius et al., 2014). We calculated separate Hg maps for sev-eral soil layers: 0–30 cm, 0–60 cm 0–100 cm, 0–300 cm, active layer, and permafrost. We assume 300 cmrepresents the typical soil accumulation since the last glacial maximum to capture 90% of the carbon inthe near surface soils. The active layer Hg extends from the surface to ALD, and the permafrost Hg extendsfrom the ALD to 300 cm. We used simulated ALD from the Community Land Model version 3.4 (Koven et al.,2015) and a linear fit of cumulative SOC with depth from the profiles in Harden et al. (2012). We ignorelocalized deposits in yedoma and deltaic soils known to extend below 300 cm. We account for the fact thatpermafrost occurs only under 50–90% of the land area in discontinuous zones and for the volume of soiltaken up by excess ground ice (Hugelius, Tarnocai, et al., 2013; Hugelius et al., 2014).

We used the median as the representative RHgC with uncertainty as the 25th to 75th percentiles. We usequadrature to combine uncertainty of RHgC with the 14.5% uncertainty in soil carbon from the NCSCD.We statistically evaluated the representativeness of the median RHgC by subdividing the data and determin-ing if the median RHgC changes between sites, depths, and soil types. We regressed RHgC against

14C age toevaluate the representativeness of the median RHgC over time. We evaluated the spatial representativenessof our measurements by comparison with 11,000 published measurements. Less than 2% of published datacome from permafrost sites, so we included data from boreal and temperate sites (Table S5 and S6). Weincluded only sites with both SOC and STHg measurements to calculate RHgC. The published data includedextreme outliers indicative of modern Hg contamination that biased the statistics. Our samples stayedfrozen for thousands of years and represent preindustrial conditions, so to make a fair comparison, weremoved outliers exceeding the mean plus 2 times the standard deviation (73 STHg and 125 RHgC values).This resulted in 11,000 published measurements of STHg, SOC, and RHgC from 4,926 different sites.

3. Results

We find a median STHg of 43 ± 30 ng Hg g soil�1 and a median representative RHgC of 1.6 ± 0.9 μg Hg g C�1

(Figure 2). For both STHg and RHgC, the median and mean values for our data match each other and thosefrom the published data within uncertainty. The published data show a higher mean RHgC because it has11% or ~1,100 STHg values greater than 200 ng Hg g soil�1, compared to one sample in our data, indicatinglocal contamination by anthropogenic sources at some sites. Our STHg data showed a bimodal distributionwith a primary peak at 40 ng Hg g soil�1 and a weaker secondary peak at 100 ng Hg g soil�1 resulting fromdata from four of the cores, indicating strong variability between sites. The published data also show

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variability between sites, but the secondary peak does not appear at all. Our data and the published databoth show a single dominant mode in RHgC, with 95.5% of the RHgC values falling between 0.0 and5.0 μg Hg g C�1.

The median RHgC of 1.6 ± 0.9 μg Hg g C�1 appears representative of site, depth, soil type, and age. STHgshowed high variability between sites, but the median RHgC is insensitive to site (Figure S21). Comparingour sites to maps of soil characteristics indicates the cores broadly represent ~69% of the soils found inAlaska (Hugelius, Tarnocai, et al., 2013; Hugelius et al., 2014). RHgC does not change with soil type: mineraland peat soils have roughly the same median RHgC. Although STHg and SOC both decrease with depth(Figures S22 and S23), RHgC is constant with depth: the RHgC median for any 20 cm range of depths is1.6 μg Hg g C�1 (Figures S24 and S25). Because age decreases exponentially with depth, SOC and STHg alsodecrease with age. However, unlike STHg and SOC, RHgC, appears constant with age (Figures S26–S29).

Maps of soil Hg show great spatial variability reflecting different sedimentation histories (Figure 3). The rela-tive uncertainty per pixel is 57%, which means there is a 95% probability that the actual value lies within±57% of our estimated value. Soils with high carbon content and high sedimentation show high Hg mass,such as the North Slope of Alaska and the Mackenzie River basin in Canada. Areas with little sedimentaryoverburden and shallow soils such as the Rocky Mountains and the Canadian Shield in North America havelow SOC and Hg. Slow decay due to freezing temperatures coupled with high sedimentation rates has buriedsubstantial amounts of carbon and Hg over much of Siberia. The active layer depth (ALD) varies from 30 cmnear the Arctic coastline to 100 cm in the southern permafrost regions, so much of the buried carbon and theHg bound to it lies frozen and preserved in permafrost. Our 0–30 cm map agrees with a published 0–30 soilHg map in areas with little sedimentary overburden but shows much higher soil Hg in areas with highsedimentation rates, particularly Siberia (Smith-Downey et al., 2010). A large pool of Hg in the active layerleaching into Arctic Rivers might explain why the permafrost-dominated terrestrial environment is thedominant source of Hg to the Arctic Ocean and why the Arctic Ocean is a net source of Hg to the Atlanticand Pacific Oceans (Fisher et al., 2012; Schuster et al., 2011; Soerensen et al., 2016).

4. Discussion

Several atmospheric Hg sources unique to the northern high latitudes have significant spatial and temporalvariability to explain STHg variability within and between cores (Fitzgerald & Lamborg, 2003). Northern borealforest fires release Hg into the atmosphere leading to spatial variability in Hg deposition (Homann et al., 2015;Rothenberg et al., 2010; Turetsky, et al., 2006). Spatial variations in temperature and moisture changemicrobial respiration rates (Wickland et al., 2006). Peaks in atmospheric Hg during summer resulting fromatmospheric mixing with ozone enhance Hg deposition (Banic et al., 2003; Sonke & Heimbürger, 2012).Springtime atmospheric Hg depletion after the polar sunrise may elevate Hg deposition to the high latitudes(Berg et al., 2008; Fitzgerald et al., 2005; Lindberg et al., 2002). Although southeast Alaska contains geologicHg deposits (Gray et al., 2000), we see no evidence of terrestrial geologic Hg sources within Alaska (Eberl,2004; Williams, 1962). Volcanic eruptions release Hg into the atmosphere, leading to variability in Hg deposi-tion (Pirrone et al., 2010; Pyle & Mather, 2003; Schuster et al., 2002), but we saw little evidence Hg deposition

Median: 1.6±0.9 Mean: 1.8±1.2

2.0±1.94.8±6.4

Here Published

Median:Mean:

Here Published43±3062±35

20±1036±37

Figure 2. Probability functions showing the fraction of values as a function of (a) STHg and (b) RHgC. Our data forpermafrost soils appear in black, and published data for mostly nonpermafrost soils appear in red.

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from volcanic ash. These depositional processes are not exclusive to the13 coring sites chosen for this study but rather inclusive to the highlatitudes of the Northern Hemisphere.

Despite these processes leading to highly variable depositional environ-ments, our STHgmeasurements appear consistent with similar measure-ments in permafrost regions. Peat deposits in Tomsk Oblast, west Siberia(Lyapina et al., 2009) show STHg values and vertical profiles similar toours. Rydberg et al. (2010) measured STHg of 40 ng Hg g soil�1 below25 cm depth, close to our median value of 43 ng Hg g soil�1. STHg inactive layer soils along a ~970 kilometer north-south transect of Alaskaranged from 100 ng Hg g soil�1 in the O horizon to 50 ng Hg g soil�1

in the A horizon (Wang et al., 2010). STHg ranged between 12 and375 ng Hg g soil�1, and RHgC varied between 1 and 11.3 μg Hg g C�1

at a sub-Antarctic site in Tierra del Fuego (Peña-Rodríguez et al., 2014).

Moreover, our STHg measurements appear consistent with publisheddata for nonpermafrost soils (Figure 4). Most of the 11,000 publisheddata fall in the temperate midlatitudes, with 2088 in boreal forests andonly 67 points in permafrost regions. Here we show a curve fit of themedian STHg as a function of SOC with the 90% envelope defined asthe 5th to 95th percentiles (Figures S30–S32). Superimposing our data

Figure 3. Maps of Hg (μg Hg m�2) in Northern Hemisphere permafrost zones for four soil layers: 0–30 cm, 0–100 cm,0–300 cm, and permafrost derived by multiplying maps of carbon from Hugelius, Tarnocai, et al. (2013) and Hugeliuset al. (2014) by the median RHgC. The permafrost map represents the Hg bound to frozen organic matter below the ALDand above 300 cm depth. The relative uncertainty is 57% for all pixels.

Figure 4. STHg as a function of SOC for our data (red dots), themedian of thepublished data (black line), and the 90% envelope of published data (greyareas). For SOC < 10%, the median STHg for the published data increaseslinearly with an R2 of 0.98. For SOC > 10%, the slope of the medianSTHg drops and the relationship weakens with an R2 of 0.56. About 90% ofour data values fall within the expected envelope of the published data(Figures S30–S32).

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indicates that 90% of our STHg measurements fall within the 90% envelope of the published data, with aslight shift toward higher STHg.

As SOC increases, STHg appears to shift from a receptor-limited regime to a flux-limited regime (Figure 4). Hgenters plants through the roots or by dry deposition from the atmosphere onto leaves (Obrist et al., 2017;Windham-Myers et al., 2009), where it attaches to appropriate receptor sites in organic molecules in placeof nutrients such as iron or magnesium. For mineral soils with SOC< 10%, the number of receptor sites limitthe Hg plants can retain, and STHg increases strongly with SOC (R2 = 0.98). For organic soils with SOC> 10%,receptor sites appear unlimited and the flux of Hg from the atmosphere limits the STHg. Since atmosphericdeposition is highly variable in space and time, the data become noisier and STHg appears nearly indepen-dent of SOC. The two regimes might explain why, like previously published data (Bargagli et al., 2007;Erickson, 2014), some sites show statistically significant correlations between STHg and SOC, whereas othersdid not. Sites with low SOC in the receptor-limited regime tended to have statistically significant correlations,while sites with organic soils in the flux-limited regime did not.

We estimate that soils in permafrost regions contain an estimated 1,656 ± 962 Gg Hg, of which half or793 ± 461 Gg Hg is frozen in permafrost (Figure 5 and Table 1). We estimate the total mass of Hg in each layerby multiplying each pixel by the grid cell area and summing across the permafrost domain. The average ofnine previously published estimates of global soil Hg is 454 ± 321, with a range from 235 to 1,000 Gg Hg(Table S7). However, these estimates generally limit soil depth to 30 cm, indicating our 0–30 cm soil Hg forpermafrost regions (347 ± 196 Gg Hg; Table 1) rivals the global soil Hg in previous estimates. These studies

leverage the known link between microbial decay and Hg release andoften rely on biogeochemical models that tend to underestimate soilHg in permafrost regions. To improve Hg estimates in permafrost soils,these models should account for the large drop in microbial activityunder freezing conditions and sedimentation processes that bury andfreeze organic matter into the permafrost. Our results indicate the activelayer alone represents the largest Hg reservoir on the planet. The activelayer and permafrost together contain nearly twice as much Hg as allother soils, the ocean, and the atmosphere combined.

Hg in permafrost soils represents an environmental risk as permafrostcontinues to thaw in the future. The turnover time associated with the

Atmosphere5

Ocean353

All Other Soils454

Marine Evasion

34

Marine Deposition

3

Terrestrial Deposition

Terrestrial Emissions

Vegetation10

2

Anthropogenic Emissions

2

0.4

0.2

Riverine Flux

BurialPermafrost793

Active Layer863

Figure 5. An updated schematic of the modern global Hg cycle with major reservoirs in white (Gg Hg) and fluxes in black(Gg Hg yr�1). Adapted from Amos et al. (2013) with the soil reservoir shown as an average of previously publishedestimates (Table S7).

Table 1Total Soil Carbon and Hg in Northern Hemisphere Permafrost Regions

Depth range (m) Soil carbon (Pg) Soil Hg (Gg Hg)

0–30 217 ± 12 347 ± 1960–60 333 ± 18 532 ± 3010–100 472 ± 27 755 ± 4270–200 827 ± 108 1323 ± 7640–300 1035 ± 150 1656 ± 962Permafrost 496 ± 72 793 ± 461Active layer 539 ± 78 863 ± 501

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microbial decay of frozen organic matter is ~14,000 years (Figure S28), making the Hg locked in permafrosteffectively stable on human time scales. However, projections indicate a 30–99% reduction in near surfacepermafrost by 2100, and, once thawed, the turnover time for microbial decay drops to ~70 years (Koven et al.,2013; Schaefer et al., 2011). This makes the reservoir of Hg in permafrost soils vulnerable to release over thenext century, with unknown consequences to the environment.

5. Summary

Wemeasured a median STHg of 43 ± 30 ng Hg g soil�1 and a median RHgC of 1.6 ± 0.9 μg Hg g C�1 based on588 samples from 13 soil permafrost cores from the interior and the North Slope of Alaska. These valuesappear consistent with published results of Hg concentrations for tundra soils and 11,000 nonpermafrost soilmeasurements from 4,926 different sites in North America and Eurasia. In a novel approach, we estimate thatthe entire Northern Hemisphere permafrost region contains 1,656 ± 962 Gg Hg, of which 793 ± 461 Gg Hg isfrozen in permafrost. Northern Hemisphere permafrost soils contain nearly twice as much Hg as all other soils,the ocean, and the atmosphere combined, indicating a need to reevaluate the role of the Arctic regions in theglobal Hg cycle. This Hg is vulnerable to release as permafrost thaws over the next century.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement bythe U.S. Government.

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AcknowledgmentsThe authors thank John Borg, JohnCrawford, and Bob Eaganhouse for dril-ling assistance. This article is dedicatedto George R. Aiken, whose 40 yearcareer as a U.S. Geological Surveyscientist was cut short with his deathfrom cancer in 2016. Without George’sfoundational scientific contributions toour knowledge of the world’s organicmatter, much of what we know aboutorganic matter would not have beenpossible, including the findings fromthis study. George is missed by toomany friends and family to count.However, his legacy as “Dr DOC”will liveon in all of us. Supporting Information(SI) are available at http://agupubs.onli-nelibrary.wiley.com/hub/journal/10.1002/(ISSN)1944-8007/. Data gener-ated for this study are available athttps://www.sciencebase.gov/catalog/domain repository and GeoPass:https://geopass.iedadata.org/josso/.Reprints and permission information areavailable at https://grl-submit.agu.org/.The authors declare no competingfinancial interests. Readers are welcometo comment on the online version ofthis paper. Correspondence and requestfor materials should be addressed topschuste@usgs.gov (https://orcid.org/0000-0002-8314-1372) or kevin.schae-fer@nsidc.org. Funding for this researchcame from the USGS NASQAN/NAWQAand CEN Programs; NASA grantsNNX10AR63G, NNX06AE65G, andNNX13AM25G; NOAA grantNA09OAR4310063; CUHK Direct grant4053206; the National Natural ScienceFoundation of China (91325202); theNational Key Scientific Research Project(2013CBA01802) by the Ministry ofScience and Technology of China; andNational Science Foundation grantARC1204167. P. S. devised and super-vised the study, drilled four cores, andsupervised all laboratory work. K. M. S.supervised the collection of the othercores and analyzed data. D. P. K., R. G. S.,K. P. W., and G. R. A. provided advice andguidance during writing. R. C. A.provided statistical support. J. F. D.analyzed and quality assured data fromtwo cores. J. D. G. and C. W. processedall the cores. G. H. led mapdevelopment. E. J. assisted with thewriting process and references. N. H. M.contributed to map development. A. G.,E. J., L. L., T. S., and T. Z. drilled one ormore cores. D. A. R. wrote the standardoperation procedure for the DMA-80,maintained the instrument, and pro-cessed and quality assured 85% of thedata.

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